I'm an
audiobook junkie and as far as professional narrators go, I think it'd be hard to replace a high-end performance with something computer generated and end up with the level of quality offered by the likes of a great narrator like Scott Brick. I mention him by name because it was him that made me realize how important good quality narration is. I had purchased a book at an airport bookstore on a whim and while waiting for a plane was so disgusted with the poor quality of the writing that I actually
threw the book out[0]. Years later, I had grabbed an audio book by an author I hadn't heard of simply because it was read by Scott Brick and recommended to "Read Next". Two hours in and I realized the book I had been enjoying so much was the same terrible book I had thrown out years before[1].
While I don't doubt it'll be possible for a computer to match it with enough input data (both in voice and human adjustment), it'll probably be a while before we'll be there and when we are there it'll likely require a lot of adjustment on the part of a professional. A big part of narration is knowing when and where a part of the story requires additional voice acting (and understanding what is required). A machine generated narration would have to understand the story sufficiently to be able to do that correctly. They might be able to get the audio to sound as good as it would sound if I narrated it, but someone with talent in the area is going to be hard to match.
All of that aside, it's getting pretty close to "good enough". When it reaches that point, my hope is more books will have audio versions available[2] and in all likelihood, some books that would have been narrated by a person today will likely be narrated by technology when it reaches that point, limiting human narration only to the top x% of books.
[0] I always resell books or donate them. This book was so bad that the half-hour it took from my life felt like a tragedy. I threw it out to prevent someone from experiencing its awfulness -- even for free.
[1] I realized it was the same book at the point a story was told that I had only read in the first book (and found mildly humorous). The reason I hated the other book was that it was written in the first person as a New York cop. I couldn't form a mental picture and the character was entirely unbelievable and one dimensional. When narrated properly, that problem was eliminated.
[2] I "speed read" (not gimmicky ... scan/skimming) and consume a ton of text. I've been doing it for 20 years or so and find it difficult to read word-for-word as is required for enjoyment of fiction, so to "force" it, I stick with audio books for fiction and love them.